Nonclogging impact crusher

ABSTRACT

A rock crusher of the type having a confined chamber in which a heavy rotor, carrying a plurality of hammers, contacts large rocks with sufficient force to fracture the rocks and to impel them against spaced parallel breaker bars for further size reduction is provided with self-cleaning features which permits it to handle wet or sticky feed stock without clogging. At least some of the active breaker bars are slowly rotated during operation of the crusher and the wall of the chamber in back of the bars is vibrated to prevent adherence or sticking of material to the bars and wall. The rotating bars may also be provided with intermeshing lobes or with scraper bars to further assist in the self-cleaning.

1 1 ma ma lulled males l alenl um... 1 n 0 m BNB 457 666 999 111 38 400062 628 209 333 e w a m R 3 ah P8 w J7 o r m N n L w w m A r H 7 B [22]Filed .llan.3, 1969 [45] Patented Sept. 28,1971

Primary Examiner- [73] Assignee New ByersCorporation Donald G. KellyAttorneys-Frank C. Rote, Jr. and John J. Murphey [54 NONCLOGGING IMPACTCRUSHElR 6 Claims, 7 Drawing Figs.

ABSTRACT: A rock crusher of the type having a confined 241/167, chamberin which a heavy rotor, carrying a plurality of ham- 241/187 mers,contacts large rocks with sufficient force to fracture the .B02c 13/09,1302c 13/282 rocks and to impel them against spaced parallel breakerbars for further size reduction is provided with self-cleaning fea- [50]FieldofSearch.........1...;.............................. 241/166, 189,285, 286,102, 88

tures which permits it to handle wet or sticky feed stock withoutclogging. At least some of the active breaker bars are slowly rotatedduring operation of the crusher and the wall of References Cited UNITEDSTATES PATENTS 6/1936 Armstrong.........,..1..,... 7/ 1961 the chamberin back of the bars is vibrated to prevent ad herence or sticking ofmaterial to the bars and wall. The rotating bars may also be providedwith intermeshing lobes or with scraper bars to further assist in theself-cleaning.

2,045,691 2,993,657 Meyer............

PATENTED SEP28 I97i SHEET 1 OF 4 ATTORNEY PATENTEU SEP28 Ian 3 606 8A0SHEET 2 0f d E a IO INVENTOR. MARK R. LANGE ij vmw (l iwowa/ ATTORNEY3,608,840 PATENTEUSEPZB'QH sum 3 UF 4 MARK R. LANGE BY (lff ATTORNEY IATENTEU SEP28 I97! SHEET b 0F 4 i'NVENTOR. MARK R. LANGE ATTORNEYNONCLOGGING INIIMYI tltllslihllt BACKGROUND OF THE INVENTION There areseveral types of machines that are used for the crushing and sizereduction of rocks including jaw crushers, gyratory crushers, conecrushers, pan crushers, roll crushers, and impact crushers. Thesevarious machines utilize different principals of operation inaccomplishing their desired objective. In an impact crusher, the rocksare struck with a sufficiently hard blow to fracture them into smallerpieces. The present invention deals with rock crushers of this type.Generally an impact crusher uses one or more rotors each having two ormore hammers evenly spaced about its periphery. The rock is fed bygravity into the rock crusher where it is struck by a rapidly movinghammer and is impelled against one or more breaker bars. These breakerbars are positioned so as to protect the walls of the chamber that wouldnormally be subjected to the greatest amount of abrasion and wear byrapidly propelled rocks. The breaker bars are generally circular and aretypically fabricated from bar stock, several inches thick, normally heattreated so as to provide a wear-resistant surface. When the size of therock is sufficiently small, it passes between the bars and falls to thebottom of the crusher where it is removed. Thus it can be seen that thespacing between the bars determines the size of the final product.

In the past, quarry rock of relatively high quality and low moisture wasused as feed stock for the crusher. This rock contained a relativelysmall amount of foreign material such as mud and clay and very littlemoisture. However, as sources of this high quality rock are slowlydepleted, it is often necessary in many locations to rework tailings andsecondary sources of ore to supply enough crushed rock to satisfycustomer demand. The alternative sources of rock normally contain ahigher portion of foreign materials or moisture, both of which tend toclog the crusher, thereby preventing proper size reduction and causing asubstantial diminution in the efficiency of the crusher.

SUMMARY OF THE INVENTION One object of the present invention is toimprove the operation and efficiency of an impact-type rock crusher.

Another object is to overcome the problems caused by wet feed andforeign materials sticking to the breaker bars and wall in a hammercrusher by rotating certain of the breaker bars and by vibrating thewall behind the breaker bars.

A further object is the provision of lobes for scrapers in conjunctionwith these rotating breaker bars to further assist in preventing thebuild up of foreign or wet materials.

These and other objects are accomplished in the manner to be hereaftermore fully described with particular reference to the drawings whichserve to characterize the invention and to show some of the preferredembodiments thereof wherein FIG. I. is a perspective elevational view ofa single-rotor impact crusher, as viewed from the side and rear of thecrusher;

FIG. 2 is a cross-sectional elevation of the crusher taken along lines22 of FIG. 1 showing the rotor, breaker bars and some of the improvedfeatures of the present invention;

FIG. 3 is an elevational view of the back of the brusher;

FIG. 4 is an enlarged partial view of a tension adjustment means for thechains used to rotate various of the breaker bars;

FIG. 5 is a partial cross-sectional view showing a further embodiment ofthe invention; I

FIG. 6 is a view taken along lines 6--6 of FIG. 5, and

FIG. 7 is a partial view showing yet another embodiment of theinvention.

The present invention relates to a rock crusher composed of a housingdefining a crushing chamber having a front feed opening therein and abackwall spaced opposite said opening. A top, sidewalls and a bottomdischarge opening complete the chamber. Rotor means within the chamberhave two or more axially extending hammers evenly spaced about theperiphery thereof. A plurality of spaced, heavy-duty breaker bars arespaced from the rotor, and are vertically positioned in front ol andspaced from the back wall to protect the same. Additional breaker barsmay extend along the top of the chamber for added protection. To preventthe accumulation of material around the breaker bars and the wall, atleast several of the more active breaker bars, i.e., those close to therotor that participate to the greatest extent in the fracturing of therocks, are slowly rotated preferably in the same direction as that ofthe rotor. At the same time the wall in back of these rotating breakerbars is vibrated at a relatively high frequency to prevent accumulationof material on the wall.

In FIG. 1 the crusher 2 is mounted on a pair of heavyduty I beams 4cross braced with additional I beams 6. The enclosed chamber has a feedchute l0, sidewalls 8 (one of which is shown), inclined wall 47, top 40,and a backwall I2. The feed chute 10 is defined by two sides 26, abackwall 13, top II and a feed opening having a chain curtain (shown inFIG. 2). A rotor shaft 14 runs in two bearings 16 which are supported inpillow blocks 18 which in turn are mounted on the framework 20 on Ibeams 4.

The sidewall 8 is composed of a plurality of plates 22, 24, 26. Thisfacilitates repair of the wall by replacement, not of the entire wallbut rather of individual plates, when they become worn or broken.

Extending through the sidewalls and generally parallel to the rotor area plurality of heavy roundl breaker bars including several bars 30 alongthe upper portion of the chamber, four rotatable bars 32A, B, C and Dalong the backwall and several bars 36 (shown in FIG. 2) along the lowerportion of the chamber. The two breaker bars 32D and 34 immediatelyabove the axis of the rotor are adapted to be moved toward or away fromthe periphery of the rotor, thereby serving as means to regulate themaximum size of product passing through the crusher. These two bars 32Dand 34 are preferably provided with a safety arrangement as generallydescribed in US. Pat. No. 3,202,368 assigned to the assignee of thepresent invention, to prevent serious damage to the crusher in the eventthat tramp iron or the like becomes jammed between the rotor and eitherone of the breaker bars.

Mounted on a platform 41 projecting from the top 40 beyond the sidewall8 of the brusher is a motor 42 which drives a gear reducer 44 by belt43. This gear reducer transmits rotary motion through shaft 46 tosprocket 48. The shaft is held in place by pillow blocks 45. Thesprocket 48 is connected by chain 50 to a similar sprocket on idlershaft 52 mounted in pillow blocks I10, 112 on the backwall I2 of thecrusher. The four rotatable breaker bars 32 A, B, C and D extend throughthe sidewall 8 of the chamber and have sprockets 54A, 54B, 54C and 54Dmounted thereon. Chain 56 passes around a second sprocket on idler shaft52 and then around sprockets 54A and C to drive breaker bars 32A and Cwhile chain 58 passes around a third sprocket 57 on idler shaft 52 andthence around sprocket 54B and 54D to rotate breaker bars 328 and 32D.Adjustment means 60 is used to regulate the adjustment of the tension onthe various chains 50, 56 and 58. A vibrator 62 is mounted on thebackwall 12 of the crusher and has an oscillator that is connected to aninner wall resiliently connected to the backwall.

FIG. 2 shows the details of the interior of the single-rotor rockcrusher of FIG. 1. The crushing chamber is generally defined by the top40 sidewall 8, backwall 12 and front 70. A feed chute 110 has anentrance 72 which is provided with a row of heavy chains 74 suspendedfrom the top 11 of the chute. These chains permit large rocks to beintroduced into the chamber and serve to keep small rocks from flyingout of the chamber after being struck by the hammers. The rotor 76contains a pair of slots 78 in which hammers 80 are positioned, and aresecurely locked by suitable means such as wedges 82 and bolts 84 detailsof which are more completely described in US. Pat. No. 3,295,773 ownedby the present assignee of the subject invention.

Below the feed opening is a feed plate 90. For best results it iscustomary for the feed plate to form an angle with the axle 14 of therotor and with the lowermost heavy duty breaker 34 of less than 180. Inthis manner, one hammer is passing through the active zone deliveringimpact blows to the incoming feed, while the other hammer is inactive.This serves to deliver the full energy of the heavy rotor to the impact.

As a rock is struck, it is thrown upwardly against the breaker bars.These bars in the impact zone can be provided with wear-resistantsleeves 31,33 which are adapted to be readily removed and replaced whenworn. Breaker bars 32 D and 34 are disposed in slots 103, 106respectively and can be moved toward or away from the rotor 76 tocontrol the size of the final product. Bars 36 located below the shaftof the rotor participate to some extent in the crushing of the rock butare generally not as active as those above the shaft. Feed stock that isreduced to a sufficiently small size passes between the breaker bars andfalls through discharge chamber 94 onto a conveyor, or the like placedbeneath the crusher.

A floating wall 100 is joined to the backwall 12 of the chamber by aplurality of elastomeric bushings 102. This floating wall is coupled tothe vibrating mechanism 104 of the vibrator 62. When wet feed or feedstock containing foreign materials such as mud and clay is beingprocessed, the material that passes through the breaker bars contacts,adheres to and builds up on the backwall, eventually blocking thepassage of properly sized material through the breaker bars and downinto the discharge chute. 94. Vibration of the floating wall 100 servesto prevent this accumulation of material on the wall. Rotation ofbreaker bars 32 A, B, C and D with the use of scrapers or lobes helps toprevent the build up of material between these breaker bars.

An electromagnetic vibrator oscillating at a maximum of 3,600 cycles perminute has been found to be satisfactory in carrying out the teaching ofthe present invention. By use of a rheostat control, this frequency canbe varied as needed. The invention is not limited to the use ofelectrically operated oscillators; instead mechanically or pneumaticallyactuated oscillators may be employed. The rubber bushings provide aconvenient and preferred means of attaching the floating wall 100 to thebackwall without transmitting the vibrations to the backwall. It shouldbe understood, however, that other means may be used to join the twowalls together.

FIG. 3 is a rear view of the rock crusher, showing the drive arrangementfor the rotating breaker bars. The speed reducer 44 is driven by belts43 connected to motor 42 immediately in back of the reducer, and in turnthe reducer drives shaft 36 secured in pillow blocks 45. On the end ofthe shaft is connected a sprocket that drives chain 50. This chainrotates idler shaft 52 mounted in a self-aligning bearing in pillowblock 110 bolted or otherwise secured to wall 12. The idler shaft passesthrough a second self-aligning bearing in pillow block 1 l2 and iscantilevered therebeyond. Connected to the projected portion of theidler shaft 52 are three sprockets. Chain 50 passes around the sprocketclosest to the wall of the crusher. The next adjacent sprocket driveschain 56, which rotates breaker bar 32A and 32C. Chain 58 revolvesaround the outermost sprocket and passes around sprockets on breakerbars 328 and 32D. Because of the high starting torque that is requiredto commence rotation of the breaker bars as well as the torque appliedby the repeated impact of rock against the breaker bars, it is necessarythat a torque control such as a torque coupling between the motor andthe load, and/or a torque control integral with the sprockets mounted onidler shaft 52 be used.

Details of the tension adjustment means, as well as the arrangement ofthe various sprockets for the rotors is shown in FIG. 4. In this figure,sprocket 57 and the other sprockets directly behind it are joined toidler shaft 52 by appropriate means such as a slotted keyway in whichkey 120 is disposed. As previously mentioned the shaft is supported intwo pillow blocks one of which 112 is shown. This pillow block ismounted to a plate 122 pivotally mounted to the sidewall of the rockcrusher by suitable means such as bolt 124 and nut. A screw adjustment126 permits adjustment of the plate 122 toward or away from sprockets 54A, B, C and D thereby providing means to readily adjust the tension onchain 56 and 58. Such adjustment means are normally necessitated by thechain becoming worn and undergoing a certain amount of elongation andstretching in use.

In a specific embodiment of the invention a five horsepower motorrotating at 1,750 r.p.m. is connected by twin V-belts to a shaft mountedspeed reducer. The input r.p.m. of the reducer is maintained at 636r.p.m. through the sheave ratios of the V-belt drive. The reducer inturn converts this input to an output speed of 25 r.p.m. through theinternal gears of the reducer. The output speed is transmitted through ashaft to an 18 tooth sprocket in the end of the shaft opposite thereducer. A chain drive from the output shaft sprocket to a similar 18tooth sprocket drives the idler shaft. Two other sprockets each having18 teeth are mounted on the idler shaft next to the existing drivensprocket. These two sprockets differ from the driven sprocket in thatthey have a torque limiting device, similar to a friction-type plateclutch. These devices protect the idler shaft and chains against thesudden change in torque caused by rocks impacting against the rotatingbreaker bars. An individual chain drive passes around each of theclutchtype sprockets and to alternative breaker bars having l8 toothsprockets on their projecting ends. The use of the clutch-type sprocketsprotects the entire system, from rotating bars to and including themotor, from excessive overload due to the surges in torque caused byrocks being disintegrated against the breaker bars. Each of theclutch-type sprockets are adjustable and their torque limit may be setas determined by existing conditions.

It should be mentioned that the motor shall mean any and all powerproducing units whatever their configuration may be. Also, the reducerindicates a means whereby the input speed is either increased ordecreased for output by whatever means necessary. The clutch-typesprockets shall be any and all means whereby the torque input or outputof the sprockets may be adjusted or limited as desired.

It has been found that the optimum results are achieved when the breakerbars rotate in the same direction as the rotor means. In mostapplications the bars would be rotated at a speed somewhere between l0and 50 r.p.m. depending upon the application. Rotation of adjacent barsin opposite directions will also help to reduce accumulation ofmaterial, but to a lesser extent than rotation in the same direction.

As herein shown, it has been found that effective cleaning isaccomplished by rotation of four breaker bars. lt should be noted,however, that this number is subject to variation depending upon thetype and nature of feed stock and the size of the crusher. In someinstances, the rotation of two breaker bars may be found effective. Inothers, it may be necessary to rotate six or more of the breaker bars.

It should be further noted that the drive arrangement can be variedwithout departing from the present invention. For example, direct drivefrom the speed reducer directly to the breaker bars is possible.Furthermore, it is not necessary to utilize two separate sets of chainsto drive alternate breaker bars. Instead, each breaker bar may beindividually driven. Alternately, all four breaker bars may be rotatedby one chain passing over multiple sprockets. Yet, another approachwould be to drive one adjacent pair of breaker bars with one chain and asecond pair with another. Chains have been found to be particularlyeffective in that they are highly efficient and are capable oftransmitting the required power in a positive manner. However, it shouldbe understood that a gear drive or other means such as V-belts can beused in place of one or more of the chains.

As a further modification it should be noted that other types of torquecontrol can be used between the motor and the load. These may beelectrical, mechanical or pneumatic.

FIGS. 5 and 6 show another embodiment of the invention constituting afurther means of preventing the build up and accumulation of foreignmaterial between and around the breaker bars and the backwall of a rockcrusher. Breaker bars 132 A, 132 B, 132 C and 132 D are mounted in andextend through suitable bearings 133. To one end of each breaker bar issecured a suitable sprocket. Chain 156 passes around the sprockets onbreaker bars 132 A and C while chain 158 passes around the sprockets onthe other two rotating breaker bars, to drive the bars in generally thesame manner as previously described. At spaced intervals along thebreaker bars within the chamber are triangular lobes 135 A, 135 B, 135 Cand 135 D. These lobes are connected to the breaker bars by welding orother suitable means. The lobes 135 B on breaker bar 132 B are adaptedto mesh with the lobes 135 A on the breaker bars 132 A and with thecorresponding breaker bars 132C. Lobes 135D on breaker bars 132 D meshwith the lobes 135 C on breaker bars 132 C. These lobes form the rockcontact surface of the breaker bars. Because of the triangular shape ofthe lobes, they create a pulsating motion during rotation of the breakerbars, insuring build up of material between the breaker bars. Lobes withother cross-sectional shapes such as square or oval can be used in placeof triangular lobes.

As a further variation, the sprockets on breaker bars 132 A and 132 Ccan have a different number of teeth than those on breaker bars 1328 and132 D or alternatively, chain 156 can move at a different speed thanchain 158 thereby providing a differential of movement between adjacentbreaker bars further assisting in the cleansing action.

Another variation, instead of lobes on the breaker bars, would be in theuse of stationary knives located in proximity to the periphery of therotating breaker bars to prevent accumulation of material thereon. Asshown in FIG. 7, these knives or scraper blades 235 are placed near theperiphery of the breaker bars 232 A, 232 B to continually remove theaccumulation of material that adheres to the breaker bars. These scraperblades generally extend the full width of the chamber and are secured tothe sides thereof by welding or other means. Alternatively, they mayextend through slots in the sides of the chamber, and may be secured bysuitable means permitting their easy removal from the chamber when notin use. Normally, they are positioned behind the breaker bars so as tobe at least partially protected from damage by flying rocks. They arepositioned as closely as possible to the breaker bars.

Although the invention has been described with reference to asingle-rotor impact crusher it should be clearly understood that it isapplicable to multiple rotor crushers and to other types of equipmentused to process ores and other materials in which there are problems ofaccumulation of material.

There are other departures that can be made in practicing the teachingsof the present invention without deviating from the teachings of thepresent invention defined by the claims appended hereto in which Iclaim:

1. In a rock crusher comprising a housing defining a confined crushingchamber having a feed opening and a backwall spaced opposite said feedopening, rotor means within said chamber having a plurality of hammersevenly spaced about the periphery thereof and a plurality of spacedbreaker bars at least some of which are in front of and spaced from saidbackwall, the improvement for preventing the accumulation of materialaround and between the breaker bars and the backwall including means forslowly rotating at least some of the adjacent breaker bars in the samedirection at a speed of between about 10 and about 50 revolutions perminute, and a floating wall spaced from and resiliently mounted to saidbackwall and a vibrator connected to said floating wall to vibrate thesame, said rotating breaker bars each provided with a plurality of lobesspaced apart from one another along the periphery of the breaker bars,with the lobes of adjacent breaker bars intermeshed with one another.

2. in a rock crusher comprising a confined chamber containing a rotorincluding a pair of hammers evenly spaced around the periphery thereof,said chamber defined by a front feed opening, a top, backwall, two sidewalls and a discharge chute below said rotor, and further including afeed chute below the feed opening for directing feed stock into contactwith the hammers of the rotor, the shaft of the rotor extending throughthe sidewalls of the chamber generally parallel to and between the feedchute and the backwall, a plurality of breaker bars extending generallyparallel to said rotor shaft with the ends thereof secured between thesidewalls, said breaker bars being spaced from one another and extendingat least vertically from a position between the rotor and the backwallup to the top of the chamber, the improvement for preventing the buildup of material around and between at least some of the breaker bars andthe backwall comprising means for rotating at least two adjacent breakerbars, at a speed of between about 10 and about 50 rpm. in the samedirection as the rotor, and a floating wall resiliently connected tosaid backwall and coupled to a source of vibration, each of saidrotating breaker bars provided with a plurality of spacedaparttriangular lobes, with the lobes of one breaker bar intermeshing withthose on the next adjacent breaker bar.

3. The improvement of claim 1 wherein these lobes in the planeperpendicular to the axis of the breaker bar are generally in the shapeof an equilateral triangle.

4. The improvement of claim 2 further defined in that one end of eachrotating breaker bar extends through and beyond one sidewall of thechamber and has a sprocket mounted thereon, and rotational movement istransmitted to the bars by a chain engaging said sprocket.

5. The improvement of claim 4 wherein said chain engages a sprocket onan idler shaft which is connected to a power source through a torquedrive and gear reducer.

6. The improvement of claim 5 wherein two breaker bars are connected bya first chain engaging a first sprocket on said idler shaft, and twoother breaker bars are connected by a second chain engaging a secondsprocket on said idler shaft and power is transmitted to the idler shaftby a chain drive from the torque drive and gear reducer.

- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 36o8,8u0 Dated September 28. 1971 Inventofls) Mark R Lange It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 60, the word "brusher" should read -crusher--. Column 2,line 42, the word "brusher" should read --crusher--. Column 3, line 54,the word "proqected" should read "projecting-- Column 4, lines 59-60,the word 'alternately" should read --alternat1ve1y--.

fiolumn 5, line 17, the phrase "insuring build up should read --insuringagainst build up--.

Signed and sealed this 21st day of March 1972.

(SEAL) Attestz' EDWARD M.FLETCHER ,JR. ROBERT GOTTSCHALK AttestingOfficer Commissioner of Patents

1. In a rock crusher comprising a housing defining a confined crushingchamber having a feed opening and a backwall spaced opposite said feedopening, rotor means within said chamber having a plurality of hammersevenly spaced about the periphery thereof and a plurality of spacedbreaker bars at least some of which are in front of and spaced from saidbackwall, the improvement for preventing the accumulation of materialaround and between the breaker bars and the backwall including means forslowly rotating at least some of the adjacent breaker bars in the samedirection at a speed of between about 10 and about 50 revolutions perminute, and a floating wall spaced from and resiliently mounted to saidbackwall and a vibrator connected to said floating wall to vibrate thesame, said rotating breaker bars each provided with a plurality of lobesspaced apart from one another along the periphery of the breaker bars,with the lobes of adjacent breaker bars intermeshed with one another. 2.In a rock crusher comprising a confined chamber containing a rotorincluding a pair of hammers evenly spaced around the periphery thereof,said chamber defined by a front feed opening, a top, backwall, two sidewalls and a discharge chute below said rotor, and further including afeed chute below the feed opening for directing feed stock into contactwith the hammers of the rotor, the shaft of the rotor extending throughthe sidewalls of the chamber generally parallel to and between the feedchute and the backwall, a plurality of breaker bars extending generallyparallel to said rotor shaft with the ends thereof secured between thesidewalls, said breaker bars being spaced from one another and extendingat least vertically from a position between the rotor and the backwallup to the top of the chamber, the improvement for preventing the buildup of material around and between at least some of the breaker bars andthe backwall comprising means for rotating at least two adjacent breakerbars, at a speed of between about 10 and about 50 r.p.m. in the samedirection as the rotor, and a floating wall resiliently connected tosaid backwall and coupled to a source of vibration, each of saidrotating breaker bars provided with a plurality of spaced-aparttriangular lobes, with the lobes of one breaker bar intermeshing withthose on the next adjacent breaker bar.
 3. The improvement of claim 1wherein these lobes in the plane perpendicular to the axis of thebreaker bar are generally in the shape of an equilateral triangle. 4.The improvement of claim 2 further defined in that one end of eachrotating breaker bar extends through and beyond one sidewall of thechAmber and has a sprocket mounted thereon, and rotational movement istransmitted to the bars by a chain engaging said sprocket.
 5. Theimprovement of claim 4 wherein said chain engages a sprocket on an idlershaft which is connected to a power source through a torque drive andgear reducer.
 6. The improvement of claim 5 wherein two breaker bars areconnected by a first chain engaging a first sprocket on said idlershaft, and two other breaker bars are connected by a second chainengaging a second sprocket on said idler shaft and power is transmittedto the idler shaft by a chain drive from the torque drive and gearreducer.